1. Field of the Invention
The present invention relates to a circulation system for supplying chemicals for manufacturing semiconductor devices and a circulating method thereof, and more particularly, to a circulation system and a circulating method for supplying and re-circulating chemicals to a processing section for manufacturing semiconductor devices, and a bypass section for collecting the chemicals while the processing section is idle.
2. Description of the Related Art
In general, a silicon substrate passes through many fabrication steps in order to form semiconductor devices thereon. These fabrication steps utilize various types of chemicals for cleaning and etching procedures that are performed during the steps. For example, a wet-etch process is performed on the semiconductor substrate having specific layers and photoresist patterns formed thereon, in which a chemical is used to etch portions of the layers to create a desired pattern. The wet-etch process is controlled by a variety of parameters, including the etch rate (the rate that a layer is etched per unit of time), the selectivity ratio (the ratio of the etch rate of the etched layer to the etch rate of its underlying layer over a certain time period), and uniformity of the etching process.
The rate of removal of material in the etch process depends on, among other parameters, the processing time, the temperature of the etching solution, and the composition of the etching solution. The accuracy to which these parameters can be controlled affects the precise amount of material removed. The etching solution can be used at room temperature, but if necessary, it can be heated or cooled in order to improve the etch rate and the efficiency of the etch process.
FIG. 1 is a schematic diagram of a conventional circulation system for supplying chemicals for manufacturing semiconductor devices. The conventional circulation system includes a chemical tank 10 containing a certain amount of etching solution comprised of a mixture of various chemicals. The chemicals are supplied from the chemical tank 10 through a chemical supply line 12 and then to a processing section where a designated manufacturing process will be performed. In this example, the processing section includes a spin chuck 22, which is rotated by the driving force of a motor 26, having a wafer to be etched loaded thereon. A chemical collection container 24 surrounds the spin-chuck 22 and collects the etching solution while the process is being carried out.
The chemical supply line 12 has a supply nozzle 20 attached at a distal end. Also, along the chemical supply line 12 there are provided, in order, a supply pump 14, a heat exchanger 16, and a cut-off valve 18. The length of the chemical supply line 12 from the front end of the heat exchanger 16 to the supply nozzle 20 is 15 m to 17 m. The portion of the chemical supply line 12 passing through the heat exchanger 16 is coil-shaped, such that the etching solution remains in the heat exchanger 16 for an extended time period. In addition, a cooling water supply may be used to further control the temperature of the etching solution passing through the chemical supply line 12.
A chemical re-circulation line 30 branches off the chemical supply line 12 at a point between the heat exchanger 16 and the cut-off valve 18, and connects to a top portion of the chemical tank 10.
A chemical collection line 28 connects the bottom of the chemical collection container 24 to a top portion of the chemical tank 10. A collection pump 29 is disposed along the chemical collection line 28.
In operation, a wafer to be etched is loaded on spin chuck 22 inside the chemical container 24, and a motor 26 is driven so as to rotate the spin chuck 22. Thereafter, supply pump 14 in the chemical supply line 12 is driven, and a certain amount of the etching solution inside the chemical tank 10 is supplied into the heat exchanger 16 via the chemical supply line 12. As the etching solution passes through the coil-shaped chemical supply line 12 in heat exchanger 16, its temperature is changed by the cooling water interacting with the heat exchanger 16.
Notice that a certain amount of the etching solution inside the heat exchanger 16 is re-circulated back to the chemical tank 10 via the chemical re-circulation line 30 by the pumping operation of the supply pump 14.
The remaining etching solution passes from the heat exchanger 16, through the cut-off valve 18, and then through the supply nozzle 20, where it is sprayed over the wafer to be etched while the wafer is rotating on the spin chuck 22. Any excess etching solution from this process is collected and stored inside the chemical collection container 24. The etching solution inside the chemical collection container 24 is re-circulated into the chemical tank 10 via the chemical collection line 28 by operating the collection pump 29 provided on the chemical collection line 28.
When the wafer etching process is completed, the cut-off valve 18 is closed and the rotation of the spin chuck 22 is stopped. A new wafer is then placed on the spin chick 22 and rotated by the motor 26, the cut-off valve 18 is then opened, and a new etching process commences.
While the new wafer is being prepared for etching, any etching solution collected and stored inside the chemical collection container 24 is re-circulated into the chemical tank 10. However, when the cut-off valve 18 is closed, some of the etching solution remains in the chemical supply line 12 between the heat exchanger 16 and the cut-off valve 18, which alters the temperature of the etching solution. When the new wafer is ready for etching and the cut-off valve is opened, the etching solution with the altered temperature is the first to contact the wafer, which could result in a process failure.
In addition, because of the coil-shape of the chemical supply line 12 inside the heat exchanger 16, the length of the chemical supply line 12 from the front end of the heat exchanger 16 to the supply nozzle 20 (15 to 17 m) is so long that the control of the pumping pressure of the etching solution supplied by the supply pump 14 is very difficult, the temperature change of the etching solution while it is passing through the chemical supply line 12 is very large, and the possibility of chemical leaks or contamination is very high.
Another drawback of the conventional system is that a large amount of time is required to re-circulate the etching solution from the heat exchanger 16, through the chemical re-circulation line 30, and into the chemical tank 10, so that the mixture efficiency of various chemicals is decreased and the uniformity of the chemical temperature in the entire circulation line is poor.